1. Field of the Invention
The present invention relates to a method of control of an air-conditioning system driven by an engine mounted in a vehicle such as an automobile, more particularly relates to a method of control of a refrigerant compressor for a refrigeration cycle of an air-conditioning system etc. and an engine itself in accordance with its operating state when fuel is cut at the time an engine decelerates.
2. Description of the Related Art
As related art for comparison with the present invention, a method of controlling the operation of a compressor for an air-conditioning system of a vehicle described in Japanese Unexamined Patent Publication (Kokai) No. 58-38350 will be explained with reference to FIG. 8. According to this method of control, basically when an engine is operating at a speed greater than a predetermined fuel cut return judgement value and a throttle valve of the engine is closed to an idling opening degree, fuel starts to be cut and the supply of fuel to the engine is stopped. Due to this, when the engine speed falls and becomes lower than the fuel cut return judgement value, the fuel cut is ended and the supply of fuel to the engine is resumed.
In this case, to prevent engine stalling, it is necessary to make the fuel cut return judgement value different between the time when a clutch provided at a power transmission system between the engine and the refrigerant compressor of the air-conditioning system is disengaged (off state of air-conditioning system) and when the clutch is engaged (on state of air-conditioning system), so when designating the fuel cut return judgement value when the air-conditioning system is off as xe2x80x9caxe2x80x9d and the fuel cut return judgement value when the air-conditioning system is on as xe2x80x9cbxe2x80x9d, the fuel cut time for when the air-conditioning system is on corresponding to the return judgement value xe2x80x9cbxe2x80x9d is made shorter than the fuel cut time for when the air-conditioning system is off corresponding to the return judgement value xe2x80x9caxe2x80x9d. The difference between these is shown as a hatched area in the xe2x80x9cFUEL CUTxe2x80x9d section of FIG. 8.
Therefore, in this related art, even in the state of use of the air-conditioning system, when the engine speed falls to an air-conditioning cut judgement value xe2x80x9ccxe2x80x9d slightly higher than the return judgement value xe2x80x9cbxe2x80x9d for when the air-conditioning system is on after a fuel cut, the clutch of the refrigerant compressor is disengaged and the air-conditioning system is stopped so as to change the fuel cut return judgement value from the return judgement value xe2x80x9cbxe2x80x9d for when the air-conditioning system is on to the return judgement value xe2x80x9caxe2x80x9d for when the air-conditioning system is off. When the engine speed falls to a return judgement value xe2x80x9caxe2x80x9d relatively low compared with the return judgement value xe2x80x9cbxe2x80x9d, the fuel cut is ended to resume the supply of fuel to the engine and the clutch of the refrigerant compressor is engaged to resume the operation of the air-conditioning system as well.
If the operation of the air-conditioning system were continued even during a fuel cut of the engine, it would be necessary to employ the return judgement value xe2x80x9cbxe2x80x9d for when the air-conditioning system is on as has been the practice in the past, so it would be necessary to shorten the fuel cut time and end the fuel cut relatively early. Compared with this, according to the above related art, the fuel cut time is increased by exactly the hatched area shown in FIG. 8. As a result, there is the advantage that the fuel cut time becomes much longer.
According to the above related art, however, while the advantage is given that the fuel cut time becomes longer, as shown by the hatched area in the xe2x80x9cA/Cxe2x80x9d section of FIG. 8, the time when the clutch of the refrigerant compressor is disengaged and the operation of the air-conditioning system is stopped after the fuel cut becomes longer than the case where such control is not performed, so the air temperature from the air-conditioning system rises by exactly Th at the maximum as shown by the bottom section of FIG. 8, so there is the problem that uncomfortable warm air flows out into the passenger compartment at a high temperature.
An object of the present invention is to provide a novel method of control of a vehicle engine and air-conditioning system able to simultaneously satisfy the two contradictory requirements of securing the cooling capacity of the air-conditioning system and preventing the flow of uncomfortable warm air into the passenger compartment and of being able to make the engine fuel cut time as long as possible even if executing a fuel cut at an engine in the state where the air-conditioning system is being used.
According to the present invention, there is provided a method of control of an air-conditioning system driven by a vehicle engine to drive a refrigerant compressor of a refrigeration cycle comprising, when it is judged by a control device that the fuel has been cut when the vehicle engine is decelerating, then an engine speed has fallen to a predetermined first judgement value, having the control device cause the amount of discharge and the torque of the refrigerant compressor to fall once, then cause these to gradually rise in a pattern of torque control of the refrigerant compressor. In this case, when it is judged by the control device that the engine speed has fallen to a predetermined first judgement value, it is also possible to cause the amount of discharge and torque of the refrigerant compressor to fall once to zero or a value close to zero, then cause these to gradually rise. Note that in the present invention, the term xe2x80x9cair-conditioning systemxe2x80x9d includes apparatuses having refrigeration cycles other than air-conditioning systems such as refrigerators.
According to the method of control of the present invention, when it is judged by the control device that a vehicle engine executes a fuel cut and then the engine speed falls to a predetermined first judgement value, the control device causes the amount of discharge and torque of the refrigerant compressor to fall once to for example zero or a value close to zero, then cause them to gradually rise again in a pattern of torque control of the refrigerant compressor. Therefore, since the operating time of the refrigerant compressor in the fuel cut time can be extended and the minimum required refrigeration capacity can be secured in the majority of the fuel cut time, the problem of warm air flowing into the passenger compartment during the fuel cut time is eliminated. Accordingly, it is possible to simultaneously respond to the contradictory requirements of securing a cooling capacity in the fuel cut time and extending the fuel cut time.
In the present invention, it is possible to have the control device end the fuel cut of the vehicle engine when it is judged by the control device that the engine speed has fallen to a predetermined second judgement value after torque control of the refrigerant compressor is started by the control device. The second judgement value is preferably set to a value changing in accordance with the magnitude of the torque of the refrigerant compressor. Further, it is preferable to decide one or both of the amount of drop of torque and a rate of rise of the refrigerant compressor in accordance with driving conditions of the vehicle when torque control of the refrigerant compressor is started including the engine speed, vehicle speed, outside temperature, and air flow rate of a blower of the air-conditioning system.
In the present invention, it is possible to use as the refrigerant compressor a compressor having a fixed displacement. In this case, it is necessary to drive the compressor by the vehicle engine through a transmission. As this transmission, it is preferable to use a continuous variable transmission able to continuously change the transmission ratio.